Ultrashort plug

ABSTRACT

An embodiment of the present invention utilizes a frac plug having an extremely short length. The extremely short length minimizes the amount of dissolvable material that must be utilized in order to maintain the physical integrity of the plug without unduly deforming the cone. Relatively uniform loading of the cone is accomplished by circumferentially locking the slip sections in place during setting. A sufficient quantity of sealing material is provided by angling the slip surface to a degree that allows a sufficient quantity of elastomer or other sealing material to be used in conjunction with backup rings to prevent the sealing material from extruding down towards the slip.

BACKGROUND

One method of completing a well is known as plug and perf. The plug and perf operation typically begins after the well has been drilled and cased. Once the operator is ready to begin the plug and perf operation a perforating tool is assembled on the surface. The perforating tool typically incorporates a plug on the lower end. The plug, once moved into position and set, will lock into the casing walls and form a fluid tight seal preventing fluid from moving past the plug. Just above the plug is a setting tool. The setting tool, once actuated, moves the plug from an unset position where the plug can be run into the well to a set position where, as previously mentioned, the plug locks into the casing and blocks fluid flow. Just above the setting tool is the perforating gun. The perforating gun usually but not always consists of one or more shaped charges that, upon detonation, will form holes in the casing wall. Any type of perforating tool may be used such as a jetting tool, etc.

After assembly, the perforating tool is run into the well to the desired depth. After reaching the desired depth, the setting tool is actuated to move the plug from its unset position to its set position locking the plug into place. The setting tool then disconnects from the plug. After disconnection, the setting tool and the perforating gun are raised to some point above the now set plug, preferably to a location adjacent to a hydrocarbon formation. The perforating gun is then actuated, forming holes or perforations through the casing wall. The perforating gun and setting tool are then usually but not always removed from the wellbore.

With the perforating gun and setting tools removed from the wellbore the well may be fractured through the perforations formed by the perforating gun. Fracturing usually occurs by pumping high-pressure fluid through the casing to the plug. Once the fluid reaches the plug it can no longer flow downward as the plug forms a fluid tight seal and is locked to the casing. High-pressure fluid then flows laterally outward through the holes in the casing. The fluid cracks and/or removes the cement adjacent to the perforations, continuing to move outward into the rock formations, fracturing the rock and allowing hydrocarbons to flow in towards the casing, once the fracking ceases.

After fracturing, the well is put on production meaning that the oil for hydrocarbons from the various formations are allowed to flow upwards through the interior of the casing to the surface. The fracturing plug which is still in place generally form a one-way barrier to fluid flow, meaning that fluid from lower in the well can typically flow upwards through the interior bore of the fracturing plug. This fluid flow from below the plug is many times able to displace the fracturing ball which is used to seal the plug against fluid flow from the surface past the plug. However, in many instances, the ball will be seated so firmly into the plug that fluid flow from below the well cannot displaced the plug or even when fluid is able to flow through the plug, the volume of the fluid flow past the plug is less than optimum, such that an operator will want to remove the plug and the ball. In some instances, after the well is fracked an operator may drill out all of the plugs. In some instances, it is preferred to allow the plugs to dissolve or to use a nonmetallic material that is easily drillable. Unfortunately, the dissolvable material usually lacks sufficient strength to be set or locked into the well casing wall with sufficient force to maintain the plug in place in the presence of a differential pressure in excess of 7500 psi and has been shown to be ineffective at a 10,000 psi differential pressure. Generally dissolvable and non-metallic materials are relatively expensive and in order to use a dissolvable or nonmetallic material, a larger amount of the dissolvable or nonmetallic material is required in order to sufficiently distribute the forces along the body of the plug in order to reach the desired differential pressure capability leading to increased costs.

SUMMARY

It is been found that by varying the of the setting cone and by controlling the circumferential distribution of the gripping elements on the slips a plug may be constructed having an overall length of less than 8 inches and a diameter of 5 inches.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-section of an embodiment of an ultrashort plug prior to setting.

FIG. 2 is an orthogonal view of a castellator.

FIG. 3 is an orthogonal view of a slip assembly.

FIG. 4 depicts a cross-section of an embodiment of an ultrashort plug after setting.

FIG. 5 depicts a cross-section of an ultrashort plug, having greater than slip height anti-extrusion rings, prior to setting.

FIG. 6 depicts a cross-section of an ultrashort plug, having greater than slip height anti-extrusion rings, after setting.

FIG. 7 depicts a cross-section of an ultrashort plug, having fold over anti-extrusion rings, prior to setting.

FIG. 8 depicts a cross-section of an ultrashort plug, having fold over anti-extrusion rings, after setting.

FIG. 9 depicts a cross-section of an ultrashort plug, having a fold over anti-extrusion ring and a greater than slip height anti-extrusion ring in combination, prior to setting.

DETAILED DESCRIPTION

The description that follows includes exemplary apparatus, methods, techniques, or instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details.

FIG. 1 depicts a cross-section of an embodiment of an ultrashort plug 10 prior to setting. The ultrashort plug 10 has a cone 20 that acts as a central mandrel for mounting the other sections of the ultrashort plug 10. The cone 20 has an upper end 35 and a lower end 36. The cone 20 has a central passageway 39. Towards the upper end of the central passageway 39 is a beveled seat that is wider on its upper end than its lower end such that an obturating device such as a ball, plug, dart, or any other means useful for blocking the flow passage may land on the seat 21 and effectively sealing the central passageway 39 against fluid flow through the central passageway 39. Towards the lower end of the central passageway 39 is a ratchet lock 24 the ratchet lock 24 may be of any type including threads such as buttress threads. The outer diameter of the cone 20 generally has about a 12° taper 41, but can be anywhere from between 10° to 15° taper.

The cone 20 has a sealing element 22 mounted on the angled portion of the radially exterior surface of the cone 20. The sealing element 22 provides a fluid tight seal about the exterior of the plug 20 once the plug 20 is set.

Just below the sealing element 22 is the slip assembly 32. The slip assembly 32 includes a number of pockets such as pocket 12, 14, and 16 each of which may contain a ceramic or other gripping elements such as gripping element 18. Other gripping elements may also include cast iron, tungsten carbide, or powdered metal. Between the sealing element 22 and the slip assembly 32 is an anti-extrusion assembly. In the depicted embodiment the anti-extrusion assembly consists of two elements 44 and 46, where elements 44 and 46 and the slip assembly 32 have essentially the same outer diameter as measured from the centerline of the cone 20. Below the cone 20 is the castelator 30. The castelator 30 includes a void 34. The void 34 is provided as space for the lower end 36 of the slip 20 to move into when the plug 10 is set. The castelator 30 includes fingers 33 equally spaced along the circumference to interact with the slip 32 to maintain circumferential positioning of the pieces of the slip 32 during setting. The collet assembly 27 is placed towards the lower end of the plug 10 and may act as a mandrel upon which the other pieces of the plug may be mounted. The collet assembly has a number of flexible collets such as collet 26 and 28. On the radially outward surface and the upper end of the collet fingers is profile 40. Profile 40 is a ratchet surface, which may be any type of threads or other surface to interact and lock into the ratchet lock 24. Typically, the castelator 30 and the collet assembly 27 are separate pieces that are attached to one another at thread 25. In some instances, the castelator 30 and the collet assembly 27 may be combined and manufactured as a single piece. Generally, when the plug 10 is assembled, a sealing element 22 is positioned on cone 20 from the lower end 36 of cone 20. Next the anti-extrusion elements 44 and 46 are positioned adjacent to the lower end of sealing element 22 on cone 20 from the lower end of cone 20. The slip 32 is then positioned adjacent the lower end of the anti-extrusion elements, in this case element 46, from the lower end 36 of cone 20. The castelator 30 is then positioned adjacent the upper end of collet assembly 27. In most instances the castelator 30 and the collet assembly 27 are attached to each other by threads 25 however in some instances the castelator 30 and the collet assembly 27 may be manufactured as a single piece in other instances the two pieces may not be attached at all such that when assembled collet assembly shoulder 51 abuts castelator assembly shoulder 53 preventing the castelator 30 from moving downward with relation to the cone 20 when the plug 10 is assembled. Generally, with the castelator 30 in position with respect to the collet assembly 27 the castelator 30 and the collet assembly 27 are moved into position so that anti-rotation elements 33 on castelator 30 interlock with the antirotation elements 19 on the slip 32 shown in FIG. 3. With the antirotation elements 33 on castelator 30 interlock with the antirotation elements 19 the collet assembly 27 and castelator 30 are moved into position with respect to slip 20 in order to hold the sealing element 22, the antiextrusion elements 44 and 46, and the slip 32 in place. Generally, the ratchet lock 24 and profile 40 interact to prevent the collet assembly 27 from moving downward with respect to cone 20 thereby keeping each of the various parts in position with respect to plug 10.

FIG. 2 is an orthogonal view of castelator 30. The castelator 30 has a number of antirotation lugs such as antirotation lug 33 and 35 that are spaced circumferentially about castelator 30. Between each of the antirotation lugs such as lug 33 and 35 is a recess such as recess 60 and recess 62.

FIG. 3 is an orthogonal view of slip 32. The slip 32 has a number of antirotation lugs such as antirotation lug 37 and 39 spaced circumferentially about slip 32. Between each of the antirotation lugs such as lug 37 and 39 is a recess such as recess 64 and recess 66. The antirotation lugs such as lug 33 and 35 on castelator 30 are circumferentially spaced and sized such that each antirotation lug on the castelator 30 will fit into the recesses on slip 32 such as recess 64 and 66. At the same time the antirotation lugs on the slip 32 such as antirotation lug 37 and 39 are spaced and sized such that each antirotation lug on the slip 32 will fit into recesses on castelator 30 such as recess 60 and 62.

FIG. 4 depicts the plug 10 in its set position. Once plug 10 is run to its desired depth the plug is set. During setting the setting tool applies force in the direction of arrow 70 against the upper end of cone 20 while at the same time the setting tool applies force in the direction of arrow 72 against collet assembly 27. As the collet assembly 27 is forced upwards with respect to cone 20, the castelator 30 is also forced upwards with respect to cone 20. As the castelator 30 moves upwards, the lower end 36 of the cone enters cavity 34. Additionally, as castelator 30 moves upwards, the slip 32 moves towards the upper end of the cone 20. However, as the slip 32 moves up the cone 20, the slip 32 is forced radially outwards. The radially outward motion of the slip causes the slip 32 to break into sections, such as sections 63 and 65, along the cutout lines, such as cutout line 19 in FIG. 3. Prior art slips were problematic in that as the slip was forced radially outward, the slip would break at the weakest point along the circumference of the slip to relieve the circumferential or hoop stress. Therefore, the prior art slips were subject to unbalanced circumferential loading of the cone. In the current embodiment as the slip 32 moves upward along cone 20 and is broken into sections such as section 63 and 65 along the cutout lines, the slip sections are held in a circumferentially spaced position about the cone 20 due to the interaction of the antirotation lugs and corresponding recesses such as the castelator antirotation lugs 33 and 35 with the corresponding slip recesses such as recess 64 and 66 as well as the interaction of the slip antirotation lugs such as antirotation lug 37 and 39 with the castelator recesses such as recess 60 and 62 which prevent the slip sections such as section 63 and 65 from moving out of their circumferentially spaced positions. With each of the slip sections such as section 63 and 65 circumferentially spaced about the cone 20, the load exerted upon the cone 20 is circumferentially distributed about the cone rather than localized loading the cone 20 which could cause failure of the cone 20.

In turn the slip 32 forces the anti-extrusion elements 44 and 46 upwards along cone 20, in turn forcing sealing element 22 upwards along cone 20. As sealing element 22 moves upwards along cone 20, sealing element 22 is forced radially outward until it ultimately contacts either the wellbore or the inner surface of a tubular within the wellbore. Once the sealing element is constrained from moving further radially outward, the sealing element will begin to extrude laterally both upwards and downwards along the plug 10. However, the anti-extrusion elements 44 and 46 are utilized to prevent the sealing element from moving downward past the anti-extrusion elements 44 and 46.

As the collet assembly 27 is moved upward with regard to cone 20, the collet fingers such as fingers 26 and 28 are pulled upwards in the interior of cone 20. As the collet fingers, such as collet fingers 26 and 28, move upwards within slip 20 the profile 40 on the radially outward surface of the collet fingers interact with the profile on ratchet lock 24 to lock the collet assembly 27 into place with regard to the cone 20. With the sealing element 22 in contact with the wellbore or tubular and in contact with the cone 20 the fluid pathway along the exterior of plug 10 is blocked. Also, with slip 32 radially extended the gripping elements 18 are in contact with the wellbore or tubular, locking the plug 10 in place within the well.

Once the plug 10 is locked into place within the wellbore or tubular a ball, dart, or other obturator may be sent through the wellbore to land on seat 21. With an obturator on seat 21, fluid flow down past the plug 10 is prevented. With fluid flow past plug 10 blocked fluid above the plug 10 within the wellbore or accessed through the wellbore may be pressurized. When in the presence of the proper fluid such as a hydrocarbon, water, acid, or other chemical the plug 10 will begin to dissolve or otherwise lose its physical integrity. At some point fluid from both above and below the plug 10 will be able to move past plug 10 without drilling or milling the plug 10.

FIG. 5 is a side view of an alternative embodiment of the ultrashort plug. In this instance plug 100 includes an alternative arrangement of the anti-extrusion assembly 151 including anti-extrusion elements 152 and 154. In this instance at least one of the anti-extrusion elements 152 or 154, and in this case both anti-extrusion elements 152 and 154, extend radially outward past the outer diameter of slip 156. Elements 154 and 152 extend a distance indicated by arrows 150 beyond the outer surface of slip 156. Additionally, each of the elements 152 and 154 has a knifepoint on its radially inward surface against cone 160. In this case anti-extrusion element 152 has knifepoint 162, anti-extrusion element 154 has a knifepoint 164. As the radially outward surface of anti-extrusion elements 152 and 154 contact the wellbore other tubular each of the knifepoints 162 and 164 will begin to dig into cone 160 and bend in a downward direction with regard to cone 160 as slip 156 forces the anti-extrusion elements 152 and 154 upwards along the cone's 160 surface. As the knifepoint 164 bends downward in relation to cone 160 the knifepoint 164 bends into a pocket 161 on the radially inward and upward surface of slip 156. With knifepoint 164 bent downward knifepoint 162 may bend downward into the void created radially inward of anti-extrusion element 154 as knifepoint 164 bends away. As knifepoints 162 and 164 bend downward in relation to slip 160 and as the radially outward surface of slip 160 has an increasing diameter as the anti-extrusion elements 152 and 154 are forced upwards along the cone 160 a barrier is formed between the radially outward surface of cone 160 and the radially inward surface of the anti-extrusion elements 152 and 154 as the knifepoint's 162 and 164 are bent downwards. While two anti-extrusion elements 152 and 154 are depicted any number of anti-extrusion elements may be used.

In some instances, it is been found that it is necessary for the anti-extrusion element to contact the inner surface of the wellbore or other tubular within which the plug 100 is located prior to the slip 156 from being fully radially outward extended. The sealing element 158 may contact the inner surface of the wellbore or other tubular and begin to extrude laterally both upwards and downwards prior to the slip 156 being fully radially extended. By having the anti-extrusion elements 152 and 154 contact the inner surface of the wellbore or other tubular prior to the slip 156 being fully extended the sealing element 158 may be prevented from extruding downward along plug 100.

FIG. 6 depicts plug 100 after setting such that sealing element 158 and slip 156 are fully in contact with the casing 157. As previously described knifepoint 164 is folded or bent downward in relation to cone 160 into pocket 161 while knife edge 162 has folded or bent downward so that knife point 162 is radially inward of anti-extrusion element 154. Together knifepoints 162 and 164 form a seal with respect to the outer surface of cone 160 and the radially outward portions of anti-extrusion elements 152 and 154 form a seal with casing 157 to prevent sealing element 158 from extruding downward toward slip 156.

FIG. 7 is a side view of an alternative embodiment of ultrashort plug 200. Here plug 200 includes an alternative embodiment of the anti-extrusion assembly 201 including anti-extrusion elements 203 and 206. In this embodiment anti-extrusion element 203 radially extends a distance 205 beyond the outer radial surface of slip 202. Additionally, anti-extrusion element 203 includes a knifepoint 214. Slip 202 includes a pocket 220 to provide space for the knifepoint 214 to fold into when the plug 200 is set. Anti-extrusion element 206 includes upper finger 208. Generally anti-extrusion element 206 is tapered from its upper end to its lower end such that the upper finger 208 has a thickness that is less than the lower portion 210 of anti-extrusion element 206. The upper finger 208 extends some distance 222 over the lower end and radially outward surface of sealing element 204. As shown, the upper finger 208 of anti-extrusion element 206 bends around the lower end and radially outward surface of sealing element 208 as a series of angles, in some instances, curves are sufficient. Anti-extrusion element 206 also includes knifepoint 212. The knifepoint 212 will generally fold into pocket 224 when the plug 200 is set. The pocket 224 is formed by knifepoint 214 radially inward of anti-extrusion element 203.

FIG. 8 depicts plug 200 after setting such that anti-extrusion elements 203 and 206 are fully in contact with the casing 230. During setting the sealing element 204 pushes the upper finger 208 of anti-extrusion element 206 radially outward causing upper finger 208 to form a metal-metal seal against the inward surface of casing 230 while constraining the sealing element 204 from extruding any further downwards towards slip 202. As previously described knifepoint 214 is folded or bent downward in relation to cone 216 into pocket 220 while knife edge 212 has folded or bent downward so that knife edge 212 is radially inward of anti-extrusion element 203.

FIG. 9 is a side view of an alternative embodiment of the plug 250. Here plug 250 includes an alternative embodiment of the anti-extrusion assembly 251 including anti-extrusion elements 252 and 254. In this embodiment anti-extrusion element 252 radially extends a distance 258 beyond the outer radial surface of slip 256. Anti-extrusion element 252 includes a knifepoint 260. Slip 256 includes a pocket 262 in order to provide space for the knifepoint 260 to fold into when the plug 250 is set. Anti-extrusion element 254 includes upper finger 264. Generally anti-extrusion element 254 is tapered across a portion of its upper end such that the upper finger 264 has a thickness that is less than the thickness of the lower portion 266 of anti-extrusion element 254. Anti-extrusion element 254 also includes knifepoint 268. The knifepoint 268 folds into pocket 270 when the plug 250 is set. The pocket 270 is formed by knifepoint 260 radially inward of anti-extrusion element 252.

The methods and materials described as being used in a particular embodiment may be used in any other embodiment. While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible.

Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter. 

What is claimed is:
 1. A wellbore plug comprising, a mandrel, an expander cone circumferentially mounted about an outer surface of the mandrel, a slip element circumferentially mounted on the outer surface of the mandrel, a sealing element circumferentially mounted on an outer surface of the expander cone, an anti-extrusion element circumferentially mounted on an outer surface of the expander cone, wherein the anti-extrusion element is axially located between the sealing element and the slip element, further wherein the anti-extrusion extends radially beyond an outer surface of the slip element.
 2. The wellbore plug of claim 1 wherein, the anti-extrusion element extends radially beyond the outer surface of the slip element by between 0.030 inches and 0.090 inches.
 3. The wellbore plug of claim 1 wherein, the anti-extrusion element extends radially beyond the outer surface of the slip element by about 0.060 inches.
 4. The wellbore plug of claim 1 wherein, the mandrel has a throughbore.
 5. The wellbore plug of claim 1 wherein, the cone increases in diameter at between an 10 and 15 degree angle from the lower end towards the upper end.
 6. The wellbore plug of claim 1 wherein, the cone increases in diameter at about a 12 degree angle from the lower end towards the upper end.
 7. The wellbore plug of claim 1 wherein, the wellbore plug has an overall length of less than 8 inches.
 8. The wellbore plug of claim 1 wherein, the mandrel includes at least two anti-rotation lugs and the slip includes at least two anti-rotation lugs; wherein the mandrel anti-rotation lugs and the slip anti rotation lugs maintain the slip in at least two circumferentially spaced positions relative to the mandrel after setting.
 9. The wellbore plug of claim 8 wherein, the mandrel anti-rotation lugs and the slip anti rotation lugs maintain the slip in a uniformly spaced position about the circumference of the mandrel after setting. 